Scattering delocalization and radiation damage in STEM-EELS

We discuss the delocalization of the inelastic scattering of 60-300 keV electrons in a thin specimen, for energy losses below 50 eV where the delocalization length exceeds atomic dimensions. Analytical expressions are derived for the point spread function (PSF) that describes the radial distribution of this scattering, based on its angular distribution and a dielectric representation of energy loss. We also compute a PSF for energy deposition, which is directly related to the radiolysis damage created by a small-diameter probe. These concepts are used to explain the damage kinetics, measured as a function of probe diameter, in various polymers. We also evaluate a “leapfrog” coarse-scanning procedure as a technique for energy-filtered imaging of a beam-sensitive specimen.